1. Field of the Invention
The present invention relates to a zoom lens device. More particularly, the present invention relates to a zoom lens device in which focusing at a wide-angle end is possible precisely even with a simple construction.
2. Description Related to the Prior Art
JP-A 4-235511 discloses a zoom lens device having plural lens groups, among which a focusing lens group is operated for focusing. An in-focus position for the focusing lens group is obtained according to a zoom position and an object distance, so as to move the focusing lens group to the in-focus position. A motor is driven to move the focusing lens group to the in-focus position. A rotary encoder is associated with the motor, detects a rotational angle of the motor, and causes the focusing lens group to be set precisely in the in-focus position by controlling the motor.
In the zoom lens device, the focusing lens group is moved to the in-focus position in consideration of an object distance of a particular object. It is general in the zoom lens device that an amount of moving the focusing lens group to the in-focus position is higher in positions near to a telephoto end than in positions near to a wide-angle end. According the prior art, resolving power of the rotary encoder is determined so as to obtain sufficiently high precision in positions near to the wide-angle end.
However, there occurs a problem in that the difference in the moving amount of the focusing lens group becomes remarkably high if a zoom ratio of the zoom lens device is high. The rotary encoder needs to be a type of high precision for the purpose of obtaining sufficient precision in positions near to the wide-angle end. This raises the manufacturing cost of the zoom lens device. Another problem occurs in that focusing may take long time because the moving amount of the focusing lens group becomes higher in positions near to the telephoto end.
According to a known type of the zoom lens device, focusing is effected by a separate advance type of barrel movement. There are a front lens group and a rear lens group in the zoom lens device disposed on the optical axis. The front and rear lens groups are moved forwards together for zooming. A distance between the front and rear lens groups is changed according to the separate advance type for the focusing operation.
Zooming and focusing are effected according to the separate advance type in the prior art. An interval between the front and rear lens groups requires changes, so as to increase the whole size of the zoom lens device. For example, the zoom lens device is zoomed out gradually from the telephoto end. The distance between the front and rear lens groups is raised for focusing, to maximize the distance between those at the wide-angle end. This requires the zoom lens device to have an extremely large size, because barrels and other elements in the zoom lens device need to be large.
In view of the foregoing problems, an object of the present invention is to provide a zoom lens device in which precise focusing at a wide-angle end is possible even with a simple construction.
Another object of the present invention is to provide a zoom lens device having a relatively small size, and also in which precise focusing is possible.
In order to achieve the above and other objects and advantages of this invention, a zoom lens device has a zoom lens device includes a zoom optical system, having at least first and second lens groups, for being set at one focal length between a wide-angle end where a focal length is short and a telephoto end where the focal length is long. A lens barrel moves in first and second regions to move the first and second lens groups along an optical axis, the lens barrel, when in the first region, focusing the zoom optical system with a predetermined focal length kept by maintaining an interval between the first and second lens groups, and when in the second region, changing the focal length of the zoom optical system. A first lens moving mechanism effects focusing by moving the first lens group relative to the second lens group along the optical axis when the lens barrel is in the second region.
Furthermore, a zoom motor moves the lens barrel. A focusing motor drives the first lens moving mechanism. A controller controls the zoom motor and the focusing motor, the controller, when the zoom optical system is set at the predetermined focal length, driving the zoom motor for focusing, and when the zoom optical system is offset from the predetermined focal length, driving the focusing motor for focusing.
The reference focal length is a focal length at the wide-angle end.
Furthermore, a rangefinding unit measures object distance. A memory stores set position information of which an address is a combination of the object distance and the focal length. The controller reads the set position information from the memory according to the object distance and the focal length, and drives the zoom motor or the focusing motor according to the set position information.
The lens barrel effects focusing operation by rotating from a starting point of the first region toward an ending point of the first region, the starting point being at the wide-angle end, and the ending point being continuous with the second region.
Furthermore, a zoom position detector detects the focal length where the zoom optical system is set.
Furthermore, a stationary barrel supports the lens barrel in a rotatable and slidable manner. At least one movable barrel is contained in the lens barrel, movable along the optical axis, for supporting the zoom optical system in a movable manner. At least one cam mechanism is actuated by rotation of the lens barrel, for moving the movable barrel along the optical axis.
The cam mechanism has first and second cam regions associated with respectively the first and second regions.
The cam mechanism includes a cam follower pin formed to project from the movable barrel. A cam groove is formed in the lens barrel, engaged with the cam follower pin, caused by rotation of the lens barrel to push the cam follower pin along the optical axis, the cam groove having first and second groove portions, the first groove portion constituting the first cam region, the second groove portion constituting the second cam region, and being inclined relative to a rotational direction of the lens barrel at a gradient higher than the first groove portion.
Furthermore, a first measuring unit measures a first shifting amount of the first lens moving mechanism. A second measuring unit measures a second shifting amount of the lens barrel. The controller stops the zoom motor or the focusing motor when respectively the first or second shifting amount comes up to a value associated with the set position information.
The zoom position detector includes a contact brush movable together with the zoom optical system. A contact point pattern includes plural contact points, is disposed inside the stationary barrel to extend along the optical axis, contacted by the contact brush, for generating a signal for representing the focal length.
The lens barrel helically moves in the stationary barrel, and the movable barrel slides in the lens barrel. Upon powering, the controller drives the zoom motor to move the lens barrel and the movable barrel to a position associated with the wide-angle end from a collapsed position disposed in a rear in the stationary barrel.
The first lens group is disposed behind the second lens group. The first lens group includes third and fourth lens groups, the fourth lens group is disposed behind the third lens group, and driven by the focusing motor.
According to another aspect of the invention, a zoom lens device includes a zoom optical system, having at least first and second lens groups, for being set at one focal length between a wide-angle end where a focal length is short and a telephoto end where the focal length is long. A lens barrel rotates in first and second regions to zoom and focus the zoom optical system, the first and second regions being defined by dividing a section to move the zoom optical system from the wide-angle end to the telephoto end, the lens barrel, when in the first region, moving the first and second lens groups with an interval between the first and second lens groups kept unchanged, and when in the second region, moving the first and second lens groups with a change in the interval.
The lens barrel, when in the first region, focuses the zoom optical system with the focal length of the wide-angle end unchanged, and when in the second region, changes the focal length and focuses the zoom optical system.
The lens barrel, when in the second region, rotates toward the telephoto end for zooming, then the lens barrel rotates toward the wide-angle end in a predetermined focusing region for focusing, and the first lens group moves at a lower speed when the lens barrel is in the focusing region than the lens barrel rotates toward the telephoto end, so as to increase an interval between the first and second lens groups.
In a preferred embodiment, a zoom lens device includes at least first and second lens groups movable along an optical axis. A first lens barrel moves along the optical axis between a wide-angle end and a telephoto end, to zoom and focus the first and second lens groups. A first lens moving mechanism is actuated while the first lens barrel moves between the wide-angle end and a predetermined zoom position, for moving the first lens group together with the first lens barrel, and actuated while the first lens barrel moves between the predetermined zoom position and the telephoto end, for moving the first lens group relative to the first lens barrel for zooming. A second lens moving mechanism is actuated while the first lens barrel moves between the wide-angle end and the predetermined zoom position, for moving the second lens group together with the first lens barrel, and actuated while the first lens barrel moves between the predetermined zoom position and the telephoto end, for moving the second lens group relative to the first lens barrel for zooming and focusing.
Furthermore, a stationary barrel is disposed outside the first lens barrel, coupled helically with the first lens barrel, for keeping the first lens barrel movable along the optical axis in rotation. A second lens barrel is disposed inside the first lens barrel, coupled helically with the first lens barrel, for sliding along the optical axis relative to the first lens barrel when the first lens barrel rotates. A third lens barrel is disposed inside the second lens barrel, for sliding along the optical axis together with the first lens barrel. A first lens holder is contained in the third lens barrel in a slidable manner, for holding the first lens group. A second lens holder is contained in the third lens barrel in a slidable manner, for holding the second lens group.
The first lens moving mechanism includes a groove, formed in the first lens holder, for extending along the optical axis, the groove having a first end located on a side of the telephoto end, and a second end located on a side of the wide-angle end. A projection is formed to project from the second lens holder, engageable with the first and second ends, for being engaged with the first end when the second lens holder is moved toward the telephoto end, to slide the first lens holder in the third lens barrel, and for being engaged with the second end when the second lens holder is moved toward the wide-angle end, to slide the first lens holder in the third lens barrel. A retention mechanism retains the first lens holder in the third lens barrel when the projection is between the first and second ends.
The second lens moving mechanism includes a cam groove formed in the first lens barrel. A cam pin is formed to project from the second lens holder, disposed through the third lens barrel and the second lens barrel, for being engaged with the cam groove.
The cam groove includes a first portion for extending in a rotational direction of the first lens barrel to set the cam pin free from being shifted, the first portion operating when the first lens barrel moves between the wide-angle end and the predetermined zoom position. A second portion extends crosswise to the rotational direction of the first lens barrel to shift the cam pin, the second portion operating when the first lens barrel moves between the predetermined zoom position and the telephoto end.